Pressure actuatable snapaction switch with slide-and cam-adjusting means

ABSTRACT

The invention relates to a snap-action switch assembly of the type having a main lever arm and an omega spring. The lever arm is acted upon by a bellows and a coil spring which are adjacently positioned on the opposite sides of a fulcrum which pivotally supports the lever arm. The omega spring engages one end of the lever arm and an adjustment feature for the omega spring is provided. The force of the omega spring can be adjusted over a relatively wide range because it does not have to perform the additional function of providing sufficient force to press the lever arm against its pivoting bearing. The adjustment means includes a slide member and a cam means accessible to an operator and for operating said slide member.

United States Patent J orgensen et al.

[54] PRESSURE ACTUATABLE SNAP- ACTION SWITCH WITH SLIDE- AND CAM-ADJUSTING MEANS [72] Inventors: Jorgen Jorgensen, Sonderborg; Nls B.

Iversen; Jens N. Andresen, both of Nordborg, all of Denmark [73] Assignee: Danloss A/S, Nordborg, Denmark [22] Filed: Jan. 15, 1970 [211 Appl. No.: 3,067

[30] Foreign Appllcatlon Prlorlty Date Feb. 14, 1969 Germany ..P 1907 426.1

[52] US. Cl ..200/83 P, 337/319, 337/320 [51] Int. Cl. ..H0lh 35/32 [58] Field of Search. ...200/83 P, 83 PA, 83 G, 83 C, 200/83 D; 337/318, 319, 320,117, 325, 323

[451 Jan. 18,1972

FOREIGN PATENTS OR APPLICATIONS Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-Wayne B. Easton [57] ABSTRACT The invention relates to a snap-action switch assembly of the type having a main lever arm and an omega spring. The lever arm is acted upon by a bellows and a coil spring which are adjacently positioned on the opposite sides of a fulcrum which pivotally supports the lever arm. The omega spring engages one end of the lever arm and an adjustment feature for the omega spring is provided. The force of the omega spring can be adjusted over a relatively wide range because it does not have to perform the additional function of providing sufficient force to press the lever arm against its pivoting bearing. The adjustment means includes a slide member and a cam means accessible to an operator and for operating said slide member.

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PATENTEnamsmz 3636287 sum 2 or 2 1.7 50 aka 52 49 I II Fig. 4

PRESSURE ACTUATABLE SNAP-ACTION SWITCH WITII SLIDE- AND CAM-ADJUSTING MEANS The invention relates to a snap-action switch comprising a main arm and an omega spring, the main arm being acted upon by a pressure-applying means, e.g., a bellows or diaphragm, and by a nominally rated spring. Such snap-action switches are used for example as thermostats or pressure influenced units for heating or refrigerating systems.

In the known snap-action switches, the main arm is mounted at one end in a fixed support, whereas the other end resiliently engages another movable part of the snap-action system, e.g., the omega spring. The pressure-applying means and the nominally rated spring are arranged on opposite sides of the main arm, so that the difference between the forces they apply acts as an actuating force on the main arm in the required manner. It is also known to arrange the pressure-applying means and the nominally rated spring coaxially with each other on one side of the main arm and to cause them to act upon a common actuating rod with the help of which the difference in force is transmitted as the actuating force to the main arm.

One of the disadvantages of these constructions is that the arrangement comprising the pressure-applying means and the nominally rated spring occupies considerable space. In the case of equipment subjected to heavy vibration, e.g., switches on vehicles, there is the danger that the main arm will spring out of its support. Difficulty also frequently arises in arranging all the parts that it is required to displace, especially adjusting screws for setting the difference, so that they are accessible from one side of the equipment.

The object of the invention is to overcome the disadvantages of the known snap-action switches and, in particular, to provide a snap-action spring of simple construction which occupies very little space and is not affected by vibration.

According to the invention this object is achieved by arranging the pressure-applying means and the nominally rated spring alongside each other, and by their acting on the main arm from the same side and pressing it against a pivotable support disposed between them on the opposite side.

In this arrangement, the forces of the pressure-applying means and the nominally rated spring counteract each other in the required manner as regards the snap-action operation. Related to the pivoting bearing of the main arm however, the forces of the pressure-applying means and the nominally rated spring are added one to the other, so that even in the event of heavy vibration, there is no danger of the main arm springing out of the bearing. Since the pressure-applying means and the nominally rated spring are arranged alongside each other, a very compact construction is obtained, the height of which is largely determined by the length of the nominally rated spring or the length of the pressure-applying means, e.g., of a bellows.

Preferably the omega spring, supported on one side at a fixed linkage point, engages one end of the main arm, and the pivoting bearing comprises means for absorbing axial forces. This results in an extremely simple snap-action system, which consists substantially of only the main arm and the omega spring. In contrast to the known snapaction switches of this kind, the force of the omega spring can be selected as required within a very much wider range, since it does not have to perform the additional function of providing sufficient force to press the main arm against its pivoting bearing.

The length of the main arm is required to exceed the sum of later decreases again. To suit this special characteristic, it is the diameters of the pressure-applying means and the expedient to keep the distance between the pressure-applying means and the pivoting bearing equal to or less than the distance between the nominally rated spring and the pivoting bearing if the pressure-applying means is positioned on that side of the main arm remote from the omega spring, whereas the distance between the pressure-applying means and the pivoting bearing should be equal to or greater than the distance between the nominally rated spring and the pivoting bearing if the pressure-applying means is disposed on that side of the main arm presented to the omega spring.

In a preferred arrangement, limiting stops a provided on both sides of the bearing on a plate supporting it. These limiting stops determine the changeover distance of the snap-action system. If the limiting stops are adjustable, e.g., take the form of adjusting screws, they can be operated from the same side of the equipment.

Furthermore, a slide carrying the fixed support for the omega spring can be provided on the plate, which slide is displaceable in the direction of the main arm by means of a cam disc. The steepness of the characteristic curve of the omega spring can be varied by the slide and thus the difference in the snap-action system inter alia can be altered. The spindle carrying the cam disc can be moved out through the plate on the same side as the adjusting screws.

In addition, there can extend through the plate and the main arm a threaded bolt which is guided in a recess in the base of the casing and which axially displaces a washer, which provides a backing for the nominally rated spring at the free end and is prevented from rotating. By turning the threaded bolt which likewise protrudes from the top of the plate, the bias of the nominally rated spring and thus the working point of the equipment can be adjusted.

In particular the washer may have a radial arm which extends through an opening in the sidewall of the casing and acts as a pointer. The particular working point to which the equipment is set can thus be read off in a simple manner.

A bellows is expediently provided at its free end with a fixing flange, which has at least two tabs whereby it extends through the base of the casing, the tabs being bent over. This constitutes a very simple possible way of securing the bellows.

A particularly space-saving form of the snap-action switch as a whole is achieved if there is provided an electrical unit which is independent of the snap-action system, comprises at least one set of contacts and is of flat construction, this unit being disposed alongside the pressure-applying means and the nominally rated spring and standing on edge parallel with the main arm. The electrical unit can project beyond the main arm lengthwise, can be broadened at that point and can carry the connectors which are then particularly readily accessible.

The actuating element for moving the contact can be fitted at that end of the main arm remote from the omega spring. At this position it is least likely to collide with the other parts of the snap-action system.

In a preferred embodiment, the electrical unit has a casing which is made of synthetic material and which is formed as a part which can be pushed into the switch casing. The whole of the mechanical part can then be fitted, the electrical unit prepared independently, and the two finally combined by pushing one into the other.

Also, there can be formed on the main arm a lug which, when a limiting value is exceeded, engages behind a swingable catch, which can be released again by a pushbutton return means. In this way the snap-action switch can be locked in one of its end positions and only released again by an operation intended for the purpose. This pushbutton return means can also extend outwards through the plate, so that the entire operating means are accessible from the same side.

The invention will now be explained in more detail by reference to an embodiment illustrated in the drawing, in which:

FIG. 1 shows an evaporator thermostat incorporating the snap-action switch of the invention,

FIG. 2 is a vertical longitudinal section in the plane of the omega spring,

FIG. 3 is a cross section just above the main am, but with the cover plate and omega spring removed,

FIG. 4 is a side view of the electrical unit in the dismantled condition,

FIG. 5 is a fragmentary illustration of a return device which locks the thermostat at a low limiting value for temperature, and

FIG. 6 shows a lever which may be used for locking the switch in the case of a maximum limiting value for temperature.

A casing 1, made of sheet metal, has a base 2, sidewalls 3, 4 and 5, and cornered portions 6 and 7. The casing is covered at the top by a plate 8 over which extends an outer cover 9. A slideover part 10 of U-shaped cross section covers the front sidewall 4, the sidewall 3 and the open side of the casing opposite this sidewall 3. The slideover part is secured to the easing 1 by a screw 11 and contains an opening 12 for accommodating a scale which comprises a slot 13 with a pointer 14 for indicating the working point.

Bent out and downwards from the plate 8 is a knife edge bearing 15 which lies against a counterbean'ng 16 on the main arm 17 of the snap-action system. One end of the main arm 17 is connected by way of a linkage point 18 to an omega spring 19, the other end of which bears against a fixed knife edge bearing 20. On one side of the bearing 15, the main arm is acted upon by a bellows 21, acting as a pressure-applying means, and on the other side of the bearing 15, it is loaded by a nominally rated spring 22. Both parts urge the main arm 17 against the bearing 15, so that the main arm cannot spring out of the bearing even if heavy vibration occurs. The omega spring 19 applies a force to the main arm 17 in the axial direction; for this reason, a raised portion is provided on the counterbearing 16 for absorbing this axial force. The knife edge bearing 20 is secured to a slide 23 which, with the help of a cam disc, can be pushed parallel with the longitudinal axis of the main arm 17. The cam disc can be displaced by means of a spindle 24. By means of this displacement, the tension of the omega spring I9 and thus the switching differential can be altered.

The bellows 21 has at its base 25 a plate 26 which carries tabs 27 on its periphery. These tabs are pushed through openings in the base 2 and then flanged over, so that the bellows is secured. Also, a union 28, leading to the interior of the bellows, extends through the base 2.

A threaded bolt 29, on the upper end of which can be fitted a rotary knob 30, extends through the plate 8 and the main arm 17. At its lower end it is guided in a depression in the base 2. At the lower end of the bolt is provided a washer 32 for backing the spring 22. The pointer 14 is constituted by the end of an upwardly bent radial am of the washer 32, which arm, by extending into the slot 13, also forms a means for preventing rotation, so that when the knob is turned, the washer is screwed or unscrewed in the axial direction and the tension of the spring 22 is thus varied. A second washer 33 is fitted between the spring and the main arm 17 at the upper end.

On both sides of the bearing 15 is an adjusting screw 34 and 35 with the help of which the swinging movement of the main arm can be set to a predetermined value.

Secured to the main arm 17 by means of the screw 36 is an actuating element 37 which acts upon the contact system. The contact system is part of electrical unit 38, which is accommodated in. a casing 39 which can be pushed in from the right in FIG. 3. The unit is widened at its right-hand end, so that the connection tab 40 and the associated screws 41 can be reached more comfortably. The corresponding cable is introduced through an opening 42 formed in the base. An earth lead can be secured to the screw 43.

The casing 39 of the electrical unit is secured to the outer casing l by means of a screw 44. The contact system itself comprises a central fixed double contact 45 and two movable outer contacts 46 and 47, each of which is secured to a contact carrier 48, 49 and 50. Contact carriers are clamped in the casing 39 and are welded on to the tabs 40 by their ends 51, bent over at right angles. The two outer contact carriers 48 and 50 have a certain degree of resilience, so that the contacts 46 and 47 are biassed on to the fixed central contact 45 in the illustrated at rest position. The spring tension can be varied with the help of an adjusting screw 52. The actuating element 37 extends into the space 53 between the two outer carriers 48 and 50, each one of the two contacts 45 or 47 being lifted from the central contact in the two end positions of the snapaction system.

If required, a catch 52 can be fitted to the bent-up tab 7 on the housing 1 by way of a link 55, which catch is urged in the anticlockwise direction by a spring 56 (FIG. 5). The main arm 17 is provided'with an angled ratchet member 57. FIG. 5 illustrates the locked position in which the ratchet member 57 engages behind a shoulder 58, so that the main arm 17 can no longer swing in the sense dictated by a rise in temperature. By depressing a knob 59, which can be pushed upwards by means of a spring 60, the catch 54 can be swung with the help of its inclined surface 61, so that the main arm 17 again moves into the effective range 62 of the catch and can execute its normal movement.

In FIG. 6 is illustrated a catch 54, a shoulder 58' on which effects locking when the effective zone 62 is left and the shoulder 58 has been reached. The snap-action system can then only operate again in a low-temperature range after the knob 59 has been actuated.

In the embodiment illustrated, the points of engagement of the pressure-applying means 21 and the nominally rated spring 22 are the same distance from the bearing 15. They therefore act on the baring 18 under identical force-transmitting conditions. The difference between the forces applied by the pressure-applying means 21 and the nominally rated spring 22 constitutes an actuating force which counteracts the force of the omega spring directed at right angles to the dead center plane; under certain conditions, the spring force of the contact carriers 48 and 50 respectively has also to be taken into account. The system remains in the prescribed position until the actuating force overcomes the strength of the omega spring; the latter then snaps over, so that the main arm 17 snaps over into the other end position which is determined by the adjusting screws 34 and 35 respectively. As soon as the pressure in the bellows 21 is so altered that the actuating force reverses its direction. and again attains the strength of the omega spring, the system snaps back into the initial position. In the present example, the snap-over movement of the omega spring occurs only on one side of the dead center plane.

All the elements to be actuated can be reached from the top, the cover 19 being removed if necessary, i.e., the rotary knob 30 for setting the working point, the adjusting screws 34 and 35 for adjusting the distance travelled by the main arm, the spindle 24 of the cam disc for altering the difference, and the pushbutton 59 for releasing the lock.

The main arm 17 does not always require to be completely flat; it may be angled if this suits the space conditions better. Two such thermostats can also be accommodated in a common casing, for example a working thermostat and a safety thermostat. Here it is expedient if the two omega springs are positioned on the inside, and the associated connections for the electrical unit are disposed on the outside.

We claim:

I. A snapaction switch assembly comprising a casing, a lever ann, pivot bearing means for pivotally connecting said lever arm to said casing, fluid pressure expansible means for applying a force to said arm in a clockwise direction relative to said pivot bearing means, spring means for applying a force to said arm in a counterclockwise direction relative to said pivot means, said forces being applied to said lever arm at points in a plane which also includes said pivot bearing means, an omega spring exerting an axially directed force on said lever arm, said expansible means and said spring means being arranged along side each other on the opposite side of said lever arm from said pivot means, an abutment element on said casing, said omega spring having the ends thereof between said abutment element and one end of said lever arm, said pivot bearing means being formed to absorb axial forces transmitted from said omega spring, a slide member carrying said abutment element, said slide member being displaceable in the direction of said lever arm, and cam means for operating said slide member.

2. A snap-action switch assembly according to claim 1 wherein said spring means is a coil spring, threaded bolt means extending through said lever arm and axially through said coil spring, bolt-bearing means in said casing engaged by said bolt means, a threaded washer engaging the end of said coil spring opposite said lever am and threadedly engaging said bolt means, and means preventing rotation of said washer relative to said casing.

3. A snapaction switch assembly according to claim 2. wherein said casing has an opening, said washer having a radially extending pointer arm extending through said casing opening.

4. A snap-action switch assembly according to claim 1 wherein said expansible means is a bellows, said bellows having tab means at the open end thereof engageable with said casing for attaching said bellows to said casing.

5. A snap-action switch assembly according to claim 4 including an electrical unit mounted in said casing and having at least one set of contacts, said electrical unit being mounted adjacent said bellows and said spring means.

I t a *8 i 

1. A snap-action switch assembly comprising a casing, a lever arm, pivot bearing means for pivotally connecting said lever arm to said casing, fluid pressure expansible means for applying a force to said arm in a clockwise direction relative to said pivot bearing means, spring means for applying a force to said arm in a counterclockwise direction relative to said pivot means, said forces being applied to said lever arm at points in a plane which also includes said pivot bearing means, an omega spring exerting an axially directed force on said lever arm, said expansible means and said spring means being arranged along side each other on the opposite side of said lever arm from said pivot means, an abutment element on said casing, said omega spring having the ends thereof between said abutment element and one end of said lever arm, said pivot bearing means being formed to absorb axial forces transmitted from said omega spring, a slide member carrying said abutment element, said slide member being displaceable in the direction of said lever arm, and cam means for operating said slide member.
 2. A snap-action switch assembly according to claim 1 wherein said spring means is a coil spring, threaded bolt means extending through said lever arm and axially through said coil spring, bolt-bearing means in said casing engaged by said bolt means, a threaded washer engaging the end of said coil spring opposite said lever arm and threadedly engaging said bolt means, and means preventing rotation of said washer relative to said casing.
 3. A snap-action switch assembly according to claim 2 wherein said casing has an opening, said washer having a radially extending pointer arm extending through said casing opening.
 4. A snap-action switch assembly according to claim 1 wherein said expansible means is a bellows, said bellows having tab means at the open end thereof engageable with said casing for attaching said bellows to said casing.
 5. A snap-action switch assembly according to claim 4 including an electrical unit mounted in said casing and having at least one set of contacts, said electrical unit being mounted adjacent said bellows and said spring means. 